The present invention relates to a method and apparatus for efficient heat and mass transfer. More particularly, the present invention relates to a method and apparatus incorporating chambers and heat transferring partitions with segmented wetting that operates with a single gas stream at nearly constant pressure. The segmented wetting of part or all of these chambers allows gas and wetting substance temperatures to be proximate and evaporating and condensing liquid temperature and concentration integrities to be maintained. A migration movement of these wetting substances from segment to segment may allow temperature and concentration gradients to be developed or maintained. The method and apparatus can be utilized as a liquid phase concentrator, a crystallizer, a purifier, a fractionator, a stripper, an absorber, a heat exchanger, a solids or gel dryer, a reactor, and as a gas cooler or heater, and can be coupled to other processes.
Earlier developments which included elements such as a moving gas having changing vapor carrying capability, or a wetted heat transferring partition, provide a background for the present invention. Apparatus and methods using a moving gas at substantially constant pressure are known. For example, U.S. Pat. Nos. 3,860,492 to Lowi, et al. and 4,636,703 to ElDifrawi, et al. teach humidification-dehumidifications in independent vessels where energy savings, generally, relate to raising incoming feed liquid temperature. U.S. Pat. No. 3,356,591 to Peterson alters process air pressures first by compressing and heating ambient air for evaporation and then a turbine to expand and cool the air for condensation. In U.S. Pat. No. 3,214,351, Lichtenstein shows that the process can allow for air recirculation in a closed system under vacuum conditions. In other closed systems, Ramsmark discloses in U.S. Pat. No. 4,243,526, an internal combustion engine driving a compressor with the first providing heat and the second a means for condensing while Grees, U.S. Pat. No. 4,310,382 teaches using the opposite sides of a heat pump for temperature differentials. Other closed systems have incorporated methods for causing the recirculating air to be of higher pressure and temperature in the evaporation vessel than in the condensation vessel. In creating these differentials, Rhoades, in U.S. Pat. No. 4,200,497, describes using a high pressure water jet and a low pressure condenser, Mock, in U.S. Pat. No. 4,276,124 describes combining a fan followed by a pressure regulator, while Pampel, U.S. Pat. No. 4,308,111 incorporates a membrane between the two functions. U.S. Pat. Nos. 3,167,488 by Malek and 4,329,205 by Tsumara, et al. teach devices without forced gas movement where transfer of condensation heat for further evaporation is provided through a succession of plates each operating at a lower temperature. An effort to obtain improved mass transfer by negating the effects of a stagnant gas has been made by Petrik, et al. in U.S. Pat. Nos. 4,329,204 and 4,402,793 by closer spacing of the parallel plates. Use of closely spaced plates is also taught by Henderyckx in U.S. Pat. No. 3,563,860 where vapors through a permeable membrane condense on a wall transmitting heat to a liquid increasing its temperature. A counter-current flow of liquid and vapor is described by Cantrell in U.S. Pat. No. 3,788,954 for separating fluids having different vapor pressures. The use of a plurality of coaxially superimposed liquid containing basins in lieu of plates is taught in U.S. Pat. No. 3,930,958 by Maruichi. The combination of a gas and a partition in a device operating at constant pressure is shown in U.S. Pat. No. 2,902,414 by Schmerzler wherein two separate air streams are utilized in separate humidification, heat exchange, and condenser functions. A distillation apparatus having chambers where liquid is evaporated and chambers or devices on which saturated air is condensed is taught in U.S. Pat. No. 3,522,151, by Dinsmore. A nonsegmented wetted heat transfer surface allowing liquid mixing is taught in U.S. Pat. No. 4,350,570 by Makstuanko, et al. in an apparatus wherein a air stream of generally low humidity is divided into primary and secondary flows with one serving to cool a separate condensation element. A nonsegmented wetted heat transfer partition adjacent a generally packed column utilizing a single gas stream wherein gas and liquid streams flow in a concurrent manner mixing temperature profiles is taught in U.S. Pat. No. 3,822,192 by Brown.
It will be apparent that no concerted effort in developing close temperature approaches of the gas streams, preservation of liquid temperatures and concentration profiles, and combining these features in an efficient energy and mass transfer method has been contemplated.
In accordance with the present invention, a transfer method and device are provided wherein all phases, liquid or gas, may operate thermally counter-currently, wherein all liquids and gases in close proximity can be maintained at relative close temperatures, and wherein concentrations are achieved by maintaining process integrity.
It is an advantage of the present invention that it can operate with a plurality of heat sources. These heat sources can include high grade heat such as steam or combustion of natural gas, or low grade heat, such as waste heat, solar energy, and surface heat of water bodies or even ambient air, and the compression of gases to provide the desired temperature increases.
It will be appreciated that costs can be quite low. The amount of heat used is minimized because the present invention can reuse this heat many times. The invention generally operates at ambient pressure, eliminating the high initial costs and maintenance associated with pressure or vacuum vessels. In addition, the heat transfer partitions can be made of inexpensive plastic film or metal foils.
The apparatus and method of the present invention can be combined with other processes. Examples include efficient reduction of salt solutions to higher concentrations such as lithium bromide reconcentration in air conditioning systems. Also, separating ammonia-water streams by stripping and vapor absorption may find application in absorption refrigeration systems. Coupling its separation capabilities in closed cycle arrangement with reverse electrodialysis, pressure retarded osmosis, or vapor pressure differential techniques offers a choice of solutions beyond the salt brine and water mixtures presently investigated to include a number of less volatile with more volatile solution combinations.
It is a further achievement that the present invention requires only minor alteration to perform a plurality of applications. For example, many applications were tested in a single laboratory model. In this model, performance factors of over 8 were achieved for desalination of brackish or sea water. Based on this data, simulations indicate performance factors ranging in excess of 40 are possible. The model also achieved reduction of sea water to almost crystalline condition, and a reduction of a potassium carbonate solution to fifty percent from twenty-five percent concentration. The same laboratory model enriched an ethanol water mixture from a 10% feed to a 41% concentrate using 1,300 Btu's per gallon compared with approximately 6,000 for standard distillation techniques. Simulation of full scale devices indicate a 10% ethanol solution may be enriched to 95% while offering a 30 times energy reduction compared with conventional distillation columns. In air management applications, the same model offered a 27 percent greater reduction in air temperature then did a conventional evaporative cooler. In another test, the model, when supplied with a 50% potassium carbonate solution as a liquid desiccant, reduced a saturated air stream to 56% relative humidity. Simulations indicate achieving dwelling comfort zone maintenance for the weather conditions of Phoenix, Ariz. and Houston, Tex. while achieving projected electrical coefficients of performances ranging from 23 to 43.